The encapsulation of various biological materials in biologically compatible materials is a technique that has been used for some time, albeit with limited success. Exemplary of the art are U.S. Pat. Nos. 5,227,298 (Weber, et al); 5,053,332 (Cook, et al); 4,997,443 (Walthall, et al); 4,971,833 (Larsson, et al); 4,902,295 (Walthall, et al); 4,798,786 (Tice, et al); 4,673,566 (Goosen, et al); 4,647,536 (Mosbach, et al); 4,409,331 (Lim); 4,392,909 (Lim); 4,352,883 (Lim); and 4,663,286 (Tsang, et al). Also of interest is copending application Ser. No. 08/483,738, now U.S. Pat. No. 5,643,569 filed Jun. 7, 1995 to Jain, et al, incorporated by reference herein. Jain, et al discusses, in some detail, the encapsulation of secretory cells in various bio-compatible materials. As discussed therein, secretory cells are cells which secrete biological products. Generally, secretory cells possess at least some properties of endocrine cells, and may generally be treated as equivalent to cells which are endocrine in nature. The copending application discusses, e.g., the encapsulation of insulin producing cells, preferably in the form of islets, into agarose-collagen beads which have also been coated with agarose. The resulting products are useful in treating conditions where a subject needs insulin therapy, such as diabetes.
The Jain, et al application discusses, in some detail, the prior approaches taken by the art in transplantation therapy. These are summarized herein as well.
Five major approaches to protecting the transplanted tissue from the host's immune response are known. All involve attempts to isolate the transplanted tissue from the host's immune system. The immunoisolation techniques used to date include: extravascular diffusion chambers, intravascular diffusion chambers, intravascular ultrafiltration chambers, microencapsulation, and macroencapsulation. All of these methods have failed, however, due to one or more of the following problems: a host fibrotic response to the implant material, instability of the implant material, limited nutrient diffusion across semi-permeable membranes, secretagogue and product permeability, and diffusion lag-time across semi-permeable membrane barriers.
For example, a microencapsulation procedure for enclosing viable cells, tissues, and other labile membranes within a semipermeable membrane was developed by Lim in 1978. (Lim, Research report to Damon Corporation (1978)). Lim used microcapsules of alginate and poly L-lysine to encapsulate the islets of Langerhans. In 1980, the first successful in vivo application of this novel technique in diabetes research was reported (Lim, et al., Science 210: 908 (1980)). The implantation of these microencapsulated islets of Langerhans resulted in sustaining a euglycemic state in diabetic animals. Other investigators, however, repeating these experiments, found the alginate to cause a tissue reaction and were unable to reproduce Lim et al's results (Lamberti, et al. Applied Biochemistry and Biotechnology 10: 101 (1984); Dupuy, et al., J. Biomed. Material and Res. 22: 1061 (1988); Weber, et al., Transplantation 49: 396 (1990); and Doon-shiong, et al., Transplantation Proceedings 22: 754 (1990)). The water solubility of these polymers is now considered to be responsible for the limited stability and biocompatibility of these microcapsules in vivo (Dupuy, et al. supra, Weber et al. supra, Doon-shiong, et al., supra, and Smidsrod, Faraday Discussion of Chemical Society 57: 263 (1974)).
Recently, Iwata et al., (Iwata, et al. Jour. Biomedical Material and Res. 26: 967 (1992)) utilized agarose for microencapsulation of allogeneic pancreatic islets and discovered that it could be used as a medium for the preparation of microbeads. In their study, 1500-2000 islets were micro-encapsulated individually in 5% agarose and implanted into streptozotocin-induced diabetic mice. The graft survived for a long period of time, and the recipients maintained normoglycemia indefinitely.
Their method, however, suffers from a number of drawbacks. It is cumbersome and inaccurate. For example, many beads remain partially coated and several hundred beads of empty agarose form. Additional time is thus required to separate encapsulated islets from empty beads. Moreover, most of the implanted microbeads gather in the pelvic cavity, and a large number of islets are required in completely coated individual beads to achieve normoglycemia. Furthermore, the transplanted beads are difficult to retrieve, tend to be fragile, and will easily release islets upon slight damage.
A macroencapsulation procedure has also been tested. Macrocapsules of various different materials, such as poly-2-hydroxyethyl-methacrylate, polyvinylchloride-c-acrylic acid, and cellulose acetate were made for the immunoisolation of islets of Langerhans. (See Altman, et al., Diabetes 35: 625 (1986); Altman, et al., Transplantation: American Society of Artificial Internal Organs 30: 382 (1984); Ronel, et al., Jour. Biomedical Material Research 17: 855 (1983); Klomp, et al., Jour. Biomedical Material Research 17: 865-871 (1983)). In all these studies, only a transitory normalization of glycemia was achieved.
Archer et al., Journal of Surgical Research 28: 77 (1980), used acrylic copolymer hollow fibers to temporarily prevent rejection of islet xenografts. They reported long-term survival of dispersed neonatal murine pancreatic grafts in hollow fibers which were transplanted into diabetic hamsters. Recently Lacy et al., Science 254: 1782-1784 (1991) confirmed their results, but found the euglycemic state to be a transient phase. They found that when the islets are injected into the fiber, they aggregate within the hollow tube with resultant necrosis in the central portion of the islet masses. The central necrosis precluded prolongation of the graft. To solve this problem, they used alginate to disperse the islets in the fiber. However, this experiment has not been repeated extensively. Therefore, the membrane's function as an islet transplantation medium in humans is questionable.
Thus, there existed a need for achieving secretory cell transplantation, and, in particular, pancreatic islet allograft and xenograft survival without the use of chronic immunosuppressive agents.
In the Jain, et al work discussed supra, the inventors reported that encapsulating secretory cells in a hydrophilic gel material results in a functional, non-immunogenic material, that can be transplanted into animals and can be stored for long lengths of time. The encapsulation of the secretory cells provided a more effective and manageable technique for secretory cell transplantation. The encapsulation technique was described as being useful to encapsulate other biological agents, such as enzymes, micro-organisms, trophic agents including recombinantly produced trophic agents, cytotoxic agents, and chemotherapeutic agents. The encapsulated biological agents were discussed as being useful to treat conditions known to respond to the biological agent.
The application does not discuss at any length the incorporation of cells which produce diffusible biological materials, the latter being useful in a therapeutic context. A distinction is made herein between secretory cells and cells which produce diffusible biological materials. The former, as per the examples given in the Jain application, refers generally to products such as hormones, cell signalling agents, etc., which are normally considered to be biological "messengers". In contrast, diffusible biological materials refers to materials such as MHC presented peptides, cell expression regulators such as suppressors, promoters, inducers, and so forth. The distinction will be seen in the field of oncology, e.g., as per the following discussion.
Extensive studies in cancer have included work on heterogeneous cell extracts, and various cellular components. Via the use of monoclonal antibodies, the art has identified relevant cancer associated antigens, e.g., GM2, TF, STn, MUC-1, and various epitopes derived therefrom. Current theory postulates that epitopes derived from these various tumor markers complex noncovalently, with MHC molecules, thereby forming an agrotype by specific cytolytic T cells. This mechanism is not unlike various mechanisms involved in the biological response to viral infections. Note in this regard, Van der Bruggen, et al., Science 254: 1643-1647 (1991); Boon, et al., U.S. Pat. No. 5,405,940, and Boon, et al., U.S. Pat. No. 5,342,774, all of which are incorporated by reference.
Additional research which parallels the work on identification of so-called cancer epitopes has focused on the regulation of cancer proliferation, such as via suppression or, more generally, biomodulation. See, e.g., Mitchell, J. Clin. Pharmacol 32: 2-9 1992); Maclean, et al., Can. J. Oncol. 4: 249-254 (1994). The aim which unites all of these diverse approaches to cancer is the modification of the host's immune response, so as to bring about some improvement in the patient's condition.
Key to all of these approaches is the activity of one or more diffusible biological products which act in concert with other materials to modulate the immune response. Boon, et al. and van der Bruggen, et al., e.g., disclose small peptide molecules. Mitchell discusses larger molecules which function, e.g., as suppressors.
One problem with all therapeutic approaches which employ these materials is the delivery of these in a safe, effective form. This is not easily accomplished. It has now been found, surprisingly, that the techniques of Jain, et al, which were so useful in the development of therapies for conditions requiring secretory cell products can now be used in other areas.
How this is accomplished is the subject of the invention, the detailed description of which follows.